I was considering one of these/UMPC as an always carry with me computer, but I'm definitely a bit concerned its [the HTC Shift] too large to be pocketable, and not big enough to be a laptop replacement. I'm pretty sure I might just go with the OQO instead, or Sony UX--though I've heard its keypad is pretty bad. The Shift has a few plusses over the OQO and UX--one huge plus the Shift has is that it has HSDPA support built in, meaning 3G over AT&T Wireless. OQO supports EVDO from Verizon and Sprint if you have them; Sony UX has EDGE only.
I'm waiting for the holidays, to try and snag any discount if possible. I know the market for these aren't huge yet so I'm not expecting any significant drop in prices.
My advice would be to evaluate exactly where you want to take it. The Shift is probably too large for a pocket, but might work well in other cases. Decide if the battery life will perform to your needs, and I would personally hold out a bit longer for the holiday discounts.
Steve